Only enable scanner entry points if the scanner activity is callable

The first time scanner is enabled via an OTA, it might be available but
due to GMSCore version mismatch might not be callable. Hence only
enable the entry points once the scanner activity is callable.

Test: Manually
Bug: 223608369
Change-Id: I755df37738aca9c8aa65d4779b3e341968d1f48d
1 file changed